Program logic bugs vs input/environmental errors

[Timon Gehr via Digitalmars-d]

On 10/06/2014 01:01 AM, Walter Bright wrote:
> On 10/5/2014 2:51 PM, Dicebot wrote:
>> On Sunday, 5 October 2014 at 20:41:44 UTC, Walter Bright wrote:
>>> On 10/5/2014 8:35 AM, Dicebot wrote:
>>>> I am fine with non-default being hard but I
>>>> want it to be still possible within legal language restricions.
>>>
>>> D being a systems language, you can without much difficulty do
>>> whatever works
>>> for you.
>>
>> Yes but it shouldn't be in undefined behaviour domain. In other words
>> there
>> needs to be a confidence that some new compiler optimization will not
>> break the
>> application completely.
>
> Relying on program state after entering an unknown state is undefined by
> definition.

What definition?

> I don't see how a language can make a statement like "it's
> probably ok".

E.g. type safety.